This project continues the investigation of the dextran-synthesising systems of cariogenic microorganisms. The systems investigated will predominantly be those of Streptococcus mutans of different degrees of cariogenicity and emphasis will be placed on a study of the action patterns of those extracellular dextransucrases involved in the synthesis of highly-branched and insoluble dextrans. The component dextransucrases of the synthetic systems will be purified, if possible, to a state of electrophoretic homogeneity using classical methods of fractionation or a method using a specific absorption of the enzyme to an insoluble dextran. The homogeneous enzyme proteins will be characterized and the kinetics and mechanism of their catalytic reactions will be studied with respect to: (1) Specificities for synthesis of different alpha-glucosyl-linkages. (2) Specificities and relative affinities for different acceptor molecules. (3) Mechanism of action. From these studies it is hoped to establish unambiguously the mechanism by which branched dextrans of high molecular weight are synthesized, and to reveal any unique features in the actions of the dextransucrases of cariogenic organisms that may relate to their pathogenicity.